The present exemplary embodiment relates to masts. It finds particular application in conjunction with telescoping masts for antennas, lights and other payloads, and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiment is also amenable to other like applications.
Telescoping masts generally include multiple tube sections that are configured to telescope or nest within each other. A drive system is typically configured to sequentially deploy and/or retract the tubes between extended and retracted configurations. Locks or latches are generally used to lock each tube to its adjacent tube or tubes when in the extended configuration.
High-end telescoping mast customers, particularly military customers, are using mechanical masts for vehicle mounted, unguyed payload elevation involving highly sensitive surveillance and targeting electronics. These electronics are often used in an attempt to view objects over very long distances and are adversely affected by poor stability. In many applications, maintaining line-of-sight to targets is very important.
There are generally two techniques used to stabilize the payload of a telescoping mast. A first technique is gyro stabilization. Gyro stabilization can be used but it adds significant weight and cost to the payload. A second technique uses sophisticated algorithms to correct the captured image and maintain sight of their “target”, but such technique is not highly effective for rapid and “unpredictable” movements.
The interaction of external forces (such as wind) and clearances in the mast joints cause rapid and “unpredictable” movements that decrease the performance of long range “viewing” payloads. These movements can be small changes in heading (north, south, east, west), commonly called rotation and/or small changes in relation to the horizon, commonly called deflection.
The current art generally attempts to limit rotational movement via direct interaction between the tubes. The bottom, or base, tube is rigidly attached to a vehicle or shelter. In the case of cylindrical tubes, all of the subsequent tubes above that tube are prevented from rotating by a raised or recessed surface that creates at least one edge along the entire length of the tubes. That edge interacts with a groove or protrusion on the mating tubes such that any two tubes can slide axially (extend/retract) relative to each other but are prevented from rotating with respect to the each other and the base tube. This is commonly called “keying” the tubes or a “key” and “keyway” arrangement. In the case of non-cylindrical tubes, the shape of the tube itself prevents rotation via interaction of the corners of tubes.
The current art similarly attempts to limit deflection via direct interaction between the tubes. Again the bottom, or base tube, is rigidly attached to a vehicle or shelter. The subsequent tubes, even when fully extended, maintain a substantial overlap. That is, each tube remains inside the tube below it by a significant percentage of its length, commonly called “lap distance”. With this lap distance and by maintaining a close fit between the outer diameter of one tube and the inner diameter of the tube below it, the amount that one tube can freely tilt with respect to the tube below it is limited.
To allow the sliding movement (extension and retraction of the mast) under reasonable manufacturing tolerances and under typical military environmental conditions (hot, cold, sand, dust, ice) clearance must be maintained between the interacting surfaces to prevent binding. That clearance directly causes increased rotation and deflection.
The locks or latches on each tube provides vertical support against the weight of the payload to keep the tube extended after it has been driven to its extended position by the mast drive system. It is generally considered desirable to have such locks be automatically driven by the normal extension/retraction of the mast so that no outside power is required (for simplicity) and no manual intervention is required (for safety and to allow remote operation). The locks are a source of noise that can, in some instances, make the mast unfit for certain applications (e.g., military application).
Current lock designs tend to be noisy, require a large space, require manual engagement, and/or require a separate power source. In addition, many lock designs only lock the tubes in the extended position.